Jurors declined to comment following the verdict, but they told the prosecutor and Layne's lawyers during a private meeting that the 911 call was critical to their decision, according to prosecutor Paul Walton.

"They said they played it over and over and over again" in the jury room, Walton said. "One of the big things they said is when you hear the shots on the (call) there's no struggle."

Layne had said she had bought a gun the previous month because she was afraid of her grandson's outbursts. Jonathan Hoffman was living with his grandparents so he could finish his senior year at his Michigan high school while his parents, who were divorcing, had moved to Arizona to get treatment for their daughter's brain tumor.

But Jonathan Hoffman had been using drugs and acting increasingly violent. He was on probation after an earlier drug overdose landed him in the hospital and had failed a drug test earlier on the day he died.

"She killed a child she was trying to protect and tried to save," her lawyer Jerome Sabbota said during closing arguments. "Don't compound the tragedy."

The jury chose a conviction of second-degree murder, an intent to kill or do great bodily harm, but decided the crime was not premeditated, a first-degree murder charge. Michigan does not have a death penalty. Layne is expected to receive the minimum sentence of 14 years in prison, prosecutors said. But she could face as much as a life term.

A 14-year term is akin to a life sentence for Layne because of her age, Sabbota said.

The verdict came after a two-week trial that brought up as many questions as it answered. Layne had no history of violence when she shot Hoffman. Other verdicts that jurors were considering included voluntary and involuntary manslaughter, a felony firearm charge and acquittal. They also convicted Layne of using a firearm during a felony, and she will be sentenced at a later date.

Prosecutors painted Layne as a calculating and controlling woman, angry that her grandson was failing high school and fed up with his drug use and belligerent attitude.

Sabbota portrayed her as a loving grandmother who was growing ever more fearful of a teen out of control.

Walton told jurors that Layne never rushed out of her West Bloomfield home despite claiming to be afraid of her grandson and never called for an ambulance to help him. She told police that she shot him after Hoffman kicked her in the chest during a heated argument in which he wanted money to flee Michigan because of the failed drug test.

But Walton pointed out that Layne never complained to police about being attacked. A hospital nurse who examined her after her arrest said Layne had no injuries and spoke lovingly about Hoffman.

Layne's husband Fred Layne, 87, attended the trial and began crying as he left the courtroom. His wife is a former teacher, mother of five and a grandmother of nine, including Jonathan Hoffman and his younger sister, Jessica.

Hoffman's father, lawyer Michael Hoffman, said he was thrilled with the verdict and said it restored his son's reputation.

"It's been tarnished in a cruel way," Michael Hoffman said.

He said his son and Sandra Layne were close, and the woman made "little bubby potatoes and brisket" for Jonathan Hoffman, her favorite grandchild. But Michael Hoffman also called her meddlesome and controlling.

He said he believes Sandra Layne killed her grandson in one last attempt to control him.